1. Field of the Invention
The present invention relates to a disk control system, a disk control device, and a disk system, and a control method for a disk control device.
2. Description of the Related Art
The I/O performance of a disk subsystem which uses magnetic disks as its storage medium is inferior to that of a main memory of a computer which uses a semiconductor storage device as its storage medium by a difference of approximately 3 to 4 digits. Efforts have been made to reduce this difference in performance, that is, to enhance the I/O performance of subsystems. One way of enhancing the I/O performance of a disk subsystem is to configure the disk subsystem such that it is structured of a plurality of magnetic disk devices and data is stored in these magnetic disk devices. Such a system is referred to as a “disk system”.
Such a technique is disclosed in Japanese Patent Application Laid-open Publication No. 2001-256003. In the technique illustrated in FIG. 4 of this publication, a host computer 50 is indirectly connected to all disk control devices 4 through an interconnection network that uses a switch.
However, in order to collectively operate a plurality of disk control devices as a single disk control device, the switch configuring the interconnection network would have to be provided with a map indicating which one of the plurality of disk control devices connected to the switch stores the data. The switch must also have functions to comprehend the command contained in an access request having been transmitted from a host computer and to specify the disk control device storing the requested data. This requires not only the channel interfaces to perform the command comprehension but also the switches connected to the channel interfaces to perform the command comprehension. As a result, the performance will be reduced, as compared with the case in which the host computer is directly connected to the disk control devices.
To address the above problems, the aforementioned Japanese Patent Application Laid-open Publication No. 2001-256003 proposes a configuration in which all shared memories or all cache memories can be accessed from all channel interfaces and disk interfaces through the interconnection network, as shown in FIG. 1 and FIG. 8 of the publication.
According to such a technique, it is possible to provide a disk control device that has a scalable configuration and can be applied to small-scale to super-large-scale configurations with a single architecture with high-reliability and high-performance.
However, the aforementioned technique has not yet been able to provide sufficient efficiencies of data transfer and read/write process. In some cases, the efficiency of the interconnection network is reduced to 50% or less due to occurrence of logical access contention. To solve this problem, it would be necessary to employ a broader bandwidth, which would lead to increased cost.